Project Abstract The rates of HIV/AIDS, other STIs, unplanned pregnancies, and dating violence among adolescents indicate the need for evidence-based, medically-accurate, comprehensive sexual health education. However, both teachers and parents face challenges in effectively teaching about sexual health and relationships leading to students receiving incomplete or inaccurate information. Young people turn to the media for information about sex, and many media messages about sex are inaccurate and unhealthy. Consumption of unhealthy media messages (e.g., those that normalize or glamorize risky sex) is related to early and risky adolescent sexual behaviors. Media literacy education (MLE), which teaches critical analysis of media messages, has been shown to be an effective intervention for changing risky health behaviors including those related to sexual health. Thus, this Phase I application proposes to develop Media Aware Sexual Health - High School (MASH-HS), an interactive web-based comprehensive sexual health MLE program, designed to develop students? critical thinking skills and promote sexual health. It is hypothesized that this program will enhance adolescents? media literacy skills, sexual health knowledge, cognitions (i.e., attitudes, self-efficacy, and norms), and behaviors regarding healthy sexual decision-making. The program will be based upon the Message Interpretation Processing model, found to be a significant mediator of effective MLE programs in reducing sexual risk behaviors. If effective, this program would be the first comprehensive sexual health, MLE intervention and the first completely web-based program on the OAH list of evidence-based sexual health programs for male and female high school students. The proposed product is highly innovative due to 1) including a broad range of sexual health topics, 2) attention to media influence, a risk factor often ignored in sexual risk prevention programs, and 3) a paradigm shift for school-based sex education away from teacher-led programming towards a self-paced, online format that enhances student learning. Phase I of this project includes two aims. The first aim is to create a prototype of the program based on expert and stakeholder feedback, focus group discussions with target informants (i.e., adolescents), and usability studies. The second aim is to conduct a pretest-posttest feasibility study of MASH-HS in eight 9th and 10th grade classrooms in schools randomly assigned to intervention (i.e., MASH-HS) and control (i.e., typical health education curriculum) (N=136 students) conditions to assess if MASH-HS meets criteria for moving on to Phase II. These methods will provide feedback about the format, goals, and content of the program, and feasibility of the program?s effectiveness for improving adolescent health outcomes. The potential commercial applications include the creation of an engaging, effective comprehensive sexual health program that can be utilized in a wide range of educational settings. One of the added benefits is that while it enhancing sexual health, it will also develop critical thinking skills, highly valued in education settings, which should contribute positively to adoption and scalability.